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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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72                                    ALASKAN GLACIER STUDIES
Pass, to the western margin at Terrace Point. Such a sudden and absolute change in a glacier in so short an interval of time had never before been observed and described, so far as we know.
From side to side, and from as far up the mountain valley as we could see, down into the alder-covered portion of the piedmont bulb, was such a sea of crevasses (PL XX) that there was no direction in which it seemed possible to cross the glacier; and even to ascend to its surface proved to be a matter of great difficulty. Where formerly there was a waste of ablation moraine, with no ice appearing in a distant view, the glacier was so profoundly broken that clear ice appeared on every hand. Much of the ablation moraine had disappeared into the crevasses and during the summer still more was thus removed, so that the glacier surface was transformed not only by the development of innumerable crevasses but also by the loss of much of its morainic veneer. Moraine still clung to the tops of the broader serac ridges, but more than half the surface was clear ice; and instead of the undulating morainic surface there were ice splinters, pinnacles, argtes, and profound crevasses extending in'all directions.
In the valley portion of the glacier there was no appearance of system in the crevassing, but beyond the mountain front, where the glacier spreads out, the crevassing assumed a crescentic form. A series of concentric gashes, with radius increasing toward the outer portion of the crevassed area, showed their crescentic form very clearly where the pure ice was opened in the dark ablation moraine, and still more clearly in the dark-green alder zone. It was almost weiid to see these ice-walled gashes rent in the soil in which dense thickets were growing, but it showed vividly on what an unstable foundation the vegetation was growing. Toward the outer margin of the broken area the crevasses gradually died out, the outermost ones being short, narrow rents. Ablation was proceeding with rapidity, the soil beneath the plants was sliding down the slopes and into the crevasses, and they were being undermined and overturned. It was evident that the alder thickets on that part of the glacier which was broken were doomed to destruction; but whether the ice would be still further broken here, or whether the area of crevassing would be extended farther into the forest-covered part of the glacier could not be foretold.
Not less remarkable were the accompanying changes along the glacier margin, on both the east and the west sides. At Terrace Point, on the western side, the ice was crowding up on the land, overriding the gravels and pushing them up in low ridges. Below Terrace Point the ice had pushed out some distance, in the low interlobate area between the Lucia and Atrevida Glaciers, overriding a camp site occupied in 1905, and forming a new lake by the extension of an ice dam across the marginal drainage of the two glaciers. The ice was also noticeably thickened; for in 1905 the Atrevida had about the same elevation as the Lucia where the two coalesced, the boundary between the two being marked by a strip of alder; but in 1906 this alder was destroyed by lateral thrust and the area of crevassed Atrevida ice was much higher than the ablation moraine of the adjoining stagnant Lucia. The thickening amounted to fully 200 feet near the boundary between the two glaciers. At the same time the crevassed Atrevida bulb extended across the interlobate section into the area of the Lucia, and, being both higher and much crevassed, it was then easy to trace the boundary between the two glaciers.
A noteworthy feature of the glacier just below Terrace Point, and thence eastward three-quarters of the distance to Amphitheatre Knob, was a roughly-crescentic area of white ice bordered on both the up-stream and down-stream sides and on both margins by